# Question 98dd6

Nov 25, 2015

$6 \cdot {10}^{23}$

#### Explanation:

You know that one mole of any substance contains exactly $6.022 \cdot {10}^{23}$ atoms or molecules of that substance - this is known as Avogadro's number.

In your case, you're dealing with a millimole, which represents the $\frac{1}{1000} \text{th}$ part of a mole.

So, if you need ${10}^{3}$ millimoles to make one mole, it follows that you'd need ${10}^{3}$ times more molecules of carbon dioxide, ${\text{CO}}_{2}$, to get $6.022 \cdot {10}^{23}$ molecules of carbon dioxide.

1color(red)(cancel(color(black)("mmole"))) * (1color(red)(cancel(color(black)("mole"))))/(10^3color(red)(cancel(color(black)("mmoles")))) * (6.022 * 10^(23)"molecules CO"_2)/(1color(red)(cancel(color(black)("mole")))) = 6.022 * 10^(23)"molecules CO"_2#

You need to round this off to one sig fig, the number of sig figs you have for the number of millimoles of ${\text{CO}}_{2}$.

${\text{no. of molecules of CO}}_{2} = \textcolor{g r e e n}{6 \cdot {10}^{23}}$